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Truck Gun options/opinions (9mm/5.56)

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#1 B+Shooter



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Posted 15 November 2017 - 11:03 PM

So I've been planning on putting a dedicated "truck" gun in my POV so I can have something more significant than my pistol.  I've been looking at many factors while looking at options.  Many of the factors are at odds with each other, so I'm aware that whatever I end up with will be a compromise.  

  • Caliber- I would like to stay in 9mm or 5.56 because that's what I have on hand at any given time. 
  • Commonality- I have AR mags and G17 mags in my patrol car/vest/sustainment gear presently
  • Price- having a $2500 rifle sitting in car unattended all the time is pretty shitty.  I've traditionally stuck with cheaper rifles for this reason.
  • Portability- a 16" barreled AR is pretty noticeable once outside the vehicle, so the smaller- the better
  • Power- it's got to be more powerful that a souped up 22lr, or what's the point?
  • ATF avoidance- I would like to avoid having a class III for a truck gun.

Basically, I've narrowed it down to a CZ Scorpion pistol with a brace, or an AR pistol.  (A Tavor would be perfect if it wasn't so freakin' expensive!)

I'm curious how much difference there is between 5.56 in a less than 10" barrel vs. defensive 9mm in longer than 6" barrel. I'm not closed off to other ideas, these options seem to be the best options so far.


Any experiences, opinions, or advice that can help? 


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#2 DStevenson


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Posted 16 November 2017 - 05:44 AM

The 9mm is still a pistol cartridge, you're just not going to have the same results at ranges outside 50 yards but if it's self defense you shouldn't need to reach out.

My personal opinion is an AR pistol is better suited for any engagements that require more impact than a pistol, and one thing I love about the AR platform is familiarity and commonality.  

You should never be at a shortage for parts and/or accessories and because of that it's almost always my goto.

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#3 pira114


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Posted 16 November 2017 - 12:42 PM

Agreed. The only thing you gain from a pistol cartridge SBR type weapon is possibly accuracy over a pistol. Otherwise, you're still just throwing pistol rounds at your problem. Still better, but not best.

To avoid SBR issues, the AR pistol seems the better compromise. Smarter people than me have stated a barrel less than 11.5 is problematic. I'll see if I can find the article I'm referring to and post it. But even at 11.5, you've got a pretty handy compact rifle to use. And much easier to conceal both in the truck, and on you. Though I'd think once you decide it's time to bring out a truck gun, concealment is much less a concern.

Edited by pira114, 16 November 2017 - 12:43 PM.

#4 pira114


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Posted 16 November 2017 - 12:55 PM

After replying to your thread, I went straight to "another forum" to find the article I was referring to and found your other thread. Haha. So I think you'll find your answer there. In fact, I think you already did. An 11.5 BCM with the LAW folding stock option is what I'd probably go with. In the older thread you mentioned there, it might be the one where the article was linked with testing on gas ports and buffers that basically said under 11.5 inches is less than reliable.

I'll still search for that article and post it here later for others to see. And please post it if you find it first, and also post whatever you go with

#5 pira114


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Posted 16 November 2017 - 07:37 PM

From BCM

Q: Why BCM chose the 11.5" SBR over the 10.5"

I get this question a lot. It is a good one. When we spec our program we can build anything we would like, so we sat down and looked at the pros and cons.


First Statement: I know a good 10.5" SBR can run very well. I personally own a semi MK18 type and it runs great. No problems.


A: Dwell time.
Dwell time is the time that your gas operated weapon maintains pressure to continue the cycling of the weapon. It primarily exsists from the time the bullet passes the gas port in the barrel to the time the bullet exits the muzzle. When you pull the trigger and fire the weapon the movement of the bolt carrier group unlocks the bolt, extracts, and ejects the spent casing. Then it cocks the weapon, feeds, chambers the next round, and then locks again. One of the thing that can make SBRs finicky is the dwell time (or lack of).


The 11.5" carbine is approximately 4% longer weapon than its' 10.5" counterpart, but this extra inch gives the barrel a 40% increase in length for dwell time. IMHO, this is an excellent trade off. This additional dwell time (all other things being equal) will allow the carbine to be more forgiving to different ammo types, extremes in air temperature, weak or worn extractor springs, worn extractors, buffer weights, etc.


Last Statement: For those folks who have a 10.5" that works very well, I would reply; me too. (see first statement)


If I had to "go to war" with a AR15 Carbine, I would grab the BCM 11.5".

Then there's this:


#6 Refleks



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Posted 25 August 2018 - 05:31 PM

I know this isn't what you want to hear, but IMO this is where 300 blackout (if you prefer the AR platform) makes sense.

You get the advantages of a pistol caliber carbine (shorter and less overt, handier in and around vehicles, and less concussion over the 11.5" 5.56) and advantages of the intermediate rifle cartridge (better penetration of vehicles and soft armor over the PCC) and ergos of the already familiar AR platform.

Nice and compact enough that if you have to move you can do so (relatively) discreetly under a jacket or in a small bag. 

The only downside is paying out the nose for ammunition.


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